Oxidative desulfurization of fuel oil

ABSTRACT

A method for purifying a sulfur-containing fuel oil comprising (a) contacting in a first reaction mixture the sulfur-containing fuel oil with a water-soluble organic acid and oxygen at a temperature in a range of from about 100° C. to about 250° C., and at a pressure in a range of from about 15 pounds per square inch to about 2500 pounds per square inch to provide a first oxidized mixture, (b) adding water to provide a biphasic mixture comprising a water-rich phase and a fuel oil-rich phase, and (c) separating the water-rich phase from the fuel oil-rich phase to provide a purified fuel oil. In one embodiment, the method may further include an oxidation catalyst. In one embodiment, the method may further include a carbonaceous promoter. In one embodiment, the sulfur-containing fuel oil may be deasphalted before contacting with the water-soluble organic acid.

BACKGROUND

The invention includes embodiments that generally relate to a method for purifying sulfur-containing fuel oil using a water-soluble organic acid and air.

Raw/fossil fuels, such as fuel oil including a crude oil and oil distillates and refinery products like gasoline, kerosene, diesel fuel, naphtha, heavy fuel oil, natural gas, liquefied natural gas and liquefied petroleum gas, and like hydrocarbons, are useful for a number of different processes, particularly as a fuel source, and most particularly for use in a power plant. Virtually all of these fuels contain relatively high levels of naturally occurring, organic sulfur compounds, such as, but not limited to, sulfides, mercaptans and thiophenes. Hydrogen generated in the presence of such sulfur compounds has a poisoning effect on catalysts used in many chemical processes, particularly catalysts used in fuel cell processes, resulting in shortening the life expectancy of the catalysts. When present in a feed stream in a fuel cell process, sulfur compounds may also poison the fuel cell stack itself. Because of the relatively high levels of sulfur compounds that may be present in many crude fuel feed streams, it is necessary that these feed streams be desulfurized.

Furthermore, desulfurization of fuels has become an important problem due to the upcoming regulatory requirements that require a reduction in current sulfur emissions. Two major tasks in the sulfur removal from fuel include (i) the deep desulfurization of diesel fuel (reducing S content from 500 parts per million to below 15 parts per million) and, (ii) sulfur removal from crude and heavy fuel oils used for energy production (reducing S content from 3-4 percent to less than 0.5 percent). Conventional hydrodesulfurization (HDS) method using hydrogen have not only been insufficient to effect the deep desulfurization of diesel fuels but are also relatively expensive for the direct sulfur removal from a crude and heavy fuel oils due to high cost of hydrogen and the use of high temperature and pressure. Alternatively oxidative desulfurization (ODS) methods using oxidants like hydrogen peroxide, molecular oxygen or ozone, require somewhat less demanding operating conditions when compared to the operating conditions employed in HDS methods. Further, where oxygen may be used as the stoichiometric oxidant, ODS methods may be cost competitive with HDS methods.

Thus, there exists a need for efficient and cost effective ODS methods for sulfur removal from fuel, to provide desulfurized fuels that meet modern engineering and regulatory standards.

BRIEF DESCRIPTION

In one embodiment, the present invention provides a method for purifying a sulfur-containing fuel oil comprising (a) contacting in a first reaction mixture the sulfur-containing fuel oil with a water-soluble organic acid and oxygen at a temperature in a range of from about 100° C. to about 250° C., and at a pressure in a range of from about 15 pounds per square inch to about 2500 pounds per square inch to provide a first oxidized mixture, (b) adding water to provide a biphasic mixture comprising a water-rich phase and a fuel oil-rich phase, and (c) separating the water-rich phase from the fuel oil-rich phase to provide a purified fuel oil.

In another embodiment, the present invention provides a method for purifying a sulfur-containing fuel oil comprising (a) contacting in a first reaction mixture the sulfur-containing fuel oil comprising dibenzothiophene, benzothiophene, alkyl substituted dibenzothiophenes, and alkyl substituted benzothiophenes with acetic acid and oxygen at a temperature in a range of from about 125° C. to about 175° C., and at a pressure in a range of from about 1500 pounds per square inch to about 2200 pounds per square inch to provide a first oxidized mixture comprising sulfoxides and sulfones of dibenzothiophene, benzothiophene, alkyl substituted dibenzothiophenes, and alkyl substituted benzothiophenes, (b) adding water to provide a biphasic mixture comprising a water-rich phase comprising at least 50 percent of the acetic acid and a fuel oil-rich phase, and (c) separating the water-rich phase from the fuel oil-rich phase to provide a purified fuel oil.

In yet another embodiment, the present invention provides a method for purifying a sulfur-containing fuel oil comprising (a) adding a diluent to the sulfur-containing fuel oil to provide a heterogeneous mixture comprising an asphaltene-rich phase and a first fuel-oil rich phase, (b) separating the asphaltene-rich phase from the first fuel-oil rich phase, (c) contacting the first fuel-oil rich phase with a water-soluble organic acid and oxygen at a temperature in a range of from about 100° C. to about 200° C., and at a pressure in a range of from about 500 pounds per square inch to about 2500 pounds per square inch to provide a first oxidized mixture, (d) adding water to provide a biphasic mixture comprising a water-rich phase and a second fuel oil-rich phase, and (e) separating the water-rich phase from the second fuel oil-rich phase to provide a purified fuel oil.

These and other features, aspects, and advantages of the present invention may be understood more readily by reference to the following detailed description.

DETAILED DESCRIPTION

In the following specification and the claims, which follow, reference will be made to a number of terms, which shall be defined to have the following meanings.

The singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.

In one embodiment, the present invention provides a method for purifying a sulfur-containing fuel oil comprising (a) contacting in a first reaction mixture the sulfur-containing fuel oil with a water-soluble organic acid and oxygen at a temperature in a range of from about 100° C. to about 250° C., and at a pressure in a range of from about 15 pounds per square inch to about 2500 pounds per square inch to provide a first oxidized mixture, (b) adding water to provide a biphasic mixture comprising a water-rich phase and a fuel oil-rich phase, and (c) separating the water-rich phase from the fuel oil-rich phase to provide a purified fuel oil.

In one embodiment, the sulfur-containing fuel oil is a crude oil, for example Saudi sweet crude oil, West Texas Intermediate crude oil, Dubai crude oil, and Brent crude oil. In an alternate embodiment, the sulfur-containing fuel oil is a crude oil, which has been subjected to asphaltene removal. In one embodiment, the sulfur-containing fuel oil is a distillate or other refinery products of a crude oil like gasoline, kerosene, diesel fuel, naphtha, heavy fuel oil, natural gas, liquefied natural gas and liquefied petroleum gas. In one embodiment, the sulfur-containing fuel oil comprises dibenzothiophene, benzothiophene, alkyl substituted dibenzothiophenes, and alkyl substituted benzothiophenes.

In one embodiment, the sulfur-containing fuel oil comprises less than 5 weight percent sulfur based on the weight of sulfur-containing fuel oil. In another embodiment, the sulfur-containing fuel oil comprises less than 3 weight percent sulfur based on the weight of sulfur-containing fuel oil. In another embodiment, the sulfur-containing fuel oil comprises less than 2 weight percent sulfur based on the weight of sulfur-containing fuel oil.

In one embodiment, the water-soluble organic acid is selected from the group consisting of acetic acid, formic acid, propionic acid, butyric acid, and mixtures of two or more of the foregoing acids. In one embodiment, the water-soluble organic acid is acetic acid.

In one embodiment, the amount of water-soluble organic acid employed in the oxidation reaction is in a range of from about 5 volume percent to about 50 volume percent based on the amount of the sulfur-containing fuel oil. In another embodiment, the amount of water-soluble organic acid employed in the oxidation reaction is in a range of from about 15 volume percent to about 35 volume percent based on the amount of the sulfur-containing fuel oil. In yet another embodiment, the amount of water-soluble organic acid employed in the oxidation reaction is in a range of from about 20 volume percent to about 30 volume percent based on the amount of the sulfur-containing fuel oil.

In another embodiment, the first reaction mixture further comprises a transition metal oxidation catalyst. In one embodiment, the transition metal oxidation catalyst comprises oxides or salts of one or more transition metals. Non-limiting examples of suitable metals that may function as the transition metal oxidation catalyst include metals selected from the group consisting of vanadium, manganese, molybdenum, tungsten, cobalt, nickel, copper, and a combination of at least two of the foregoing metals. In one embodiment, the transition metal oxidation catalyst comprises an oxide or a salt of copper.

In yet another embodiment, the transition metal oxidation catalyst is supported on a metal oxide. Non-limiting examples of suitable metal oxide supports include silica, alumina, titania, ceria, and a combination of at least two of the foregoing metal oxides. In one embodiment, the metal oxide support is silica. In another embodiment, the metal oxide support is alumina.

In one embodiment, the transition metal oxidation catalyst comprises an active metal component which is present in an amount corresponding to from about 1 weight percent to about 10 weight percent based on the weight of the support. In another embodiment, the transition metal oxidation catalyst comprises an active metal component which is present in an amount corresponding to from about 2 weight percent to about 8 weight percent based on the weight of the support. In one embodiment, the transition metal oxidation catalyst comprises an active metal component which is present in an amount corresponding to from about 4 weight percent to about 6 weight percent based on the weight of the support.

In one embodiment, when the amount of active metal component is in a range of from about 1 weight percent to about 10 weight percent based on the support, the amount of transition metal oxidation catalyst on the metal oxide support employed in the oxidation reaction is in a range of from about 0.25 weight percent to about 10 weight percent based on the amount of the sulfur-containing fuel oil. In another embodiment, the amount of transition metal oxidation catalyst on the metal oxide support employed in the oxidation reaction is in a range of from about 0.5 weight percent to about 8 weight percent based on the amount of the sulfur-containing fuel oil. In yet another embodiment, the amount of transition metal oxidation catalyst on the metal oxide support employed in the oxidation reaction is in a range of from about 1 weight percent to about 5 weight percent based on the amount of the sulfur-containing fuel oil. One skilled in the art can easily determine the amount of metal catalyst on a metal oxide support required for the oxidation reaction based on the amount active metal content present in the metal oxide support and the amount of sulfur-containing fuel oil being purified

In another embodiment, the first reaction mixture comprises a carbonaceous promoter. In one embodiment, the carbonaceous promoter comprises activated carbon. Activated carbon represents a class of carbonaceous promoters. In one embodiment, the carbonaceous promoter is characterized by an exceptionally high surface area, as in for example, Norit activated carbon PAC-20B. In one embodiment, the carbonaceous promoter has a surface area in a range of from about 400 square meters per gram to about 1800 square meters per gram. In another embodiment, the carbonaceous promoter has a surface area in a range of from about 500 square meters per gram to about 1300 square meters per gram. In yet another embodiment, the carbonaceous promoter has a surface area in a range of from about 800 square meters per gram to about 1200 square meters per gram.

In one embodiment, the amount of carbonaceous promoter employed in the oxidation reaction is in a range of from about 1 weight percent to about 25 weight percent based on the amount of the sulfur-containing fuel oil. In another embodiment, the amount of carbonaceous promoter employed in the oxidation reaction is in a range of from about 2 weight percent to about 15 weight percent based on the amount of the sulfur-containing fuel oil. In yet another embodiment, the amount of carbonaceous promoter employed in the oxidation reaction is in a range of from about 3 weight percent to about 10 weight percent based on the amount of the sulfur-containing fuel oil. One skilled in the art can easily determine the amount of carbonaceous promoter required for the oxidation reaction based on the amount of sulfur-containing fuel oil being purified.

In one embodiment, the pressure at which the oxidation (also referred to as contacting the fuel oil with a water-soluble organic acid and oxygen at a temperature in a range of from about 100° C. to about 250° C., and at a pressure in a range of from about 15 pounds per square inch to about 2500 pounds per square inch to provide a first oxidized mixture) is carried out is in range of from about 15 pounds per square inch to about 2400 pounds per square inch. In another embodiment, the pressure at which the oxidation is carried out is in range of from about 1000 pounds per square inch to about 2250 pounds per square inch. In yet another embodiment, the pressure at which the oxidation is carried out is in range of from about 1800 pounds per square inch to about 2200 pounds per square inch.

In one embodiment, the temperature at which the oxidation is carried out is in a range from about 120° C. to about 240° C. In another embodiment, the temperature at which the oxidation is carried out is in a range from about 125° C. to about 220° C. In yet another embodiment, the temperature at which the oxidation is carried out is in a range from about 130° C. to about 200° C.

In one embodiment, the oxygen required for contacting the sulfur-containing fuel oil is provided as a mixture with an inert gas. Non-limiting suitable examples of gases suitably inert to the conditions employed include nitrogen and argon. In one embodiment, the oxygen is provided as air.

In one embodiment, the water-rich phase comprises at least 50 percent of the water-soluble organic acid. In another embodiment, the water-rich phase comprises at least 70 percent of the water-soluble organic acid. In yet another embodiment, the water-rich phase comprises at least 85 percent of the water-soluble organic acid.

In one embodiment, the method for purifying the sulfur-containing fuel oil further comprises a step of recovering the water-soluble organic acid from the water-rich phase. In one embodiment, the water-soluble organic acid is recovered from the water-rich phase by distillation using methods known to one skilled in the art.

In one embodiment, the at least one oxidized sulfur compound may be separated from the first oxidized mixture using a solid-liquid extraction process, for example an adsorption process, to provide the purified fuel oil. In one embodiment, the at least one oxidized sulfur compound may be separated from the first oxidized mixture using a liquid-liquid extraction process, to provide the purified fuel oil. One skilled in the art can easily determine the process and the conditions required to achieve satisfactory separation.

In one embodiment, when a binary catalyst is employed in the method for purifying the sulfur-containing fuel oil, the purification method further comprises a step of recovering the binary catalyst. In one embodiment, the binary catalyst is recovered from the first oxidized mixture by filtration or centrifuging/decantation, using methods known to one skilled in the art.

In one embodiment, when a carbonaceous promoter is employed in the method for purifying the sulfur-containing fuel oil, the purification method further comprises a step of recovering the carbonaceous promoter. In one embodiment, the carbonaceous promoter is recovered from the first oxidized mixture by filtration or centrifuging/decantation, using methods known to one skilled in the art.

In one embodiment, the first oxidized mixture is contacted with a porous silica adsorbent material, wherein the adsorbent material is characterized by a Brunauer-Emmett-Teller (BET) surface area value (total) of at least about 15 m²/g; and a Barrett-Joyner-Halenda (BJH) pore volume (total) of at least about 0.5 cc/g. Such porous adsorbent materials and their use are described in copending U.S. patent application Ser. No. 11/934,298 filed Nov. 2, 2007 which is incorporated herein by reference in its entirety. In instances wherein the sulfur-containing fuel oil comprises other metallic impurities such as vanadium compounds, such contact results in removal of these other metallic impurities or their oxidation products from the first oxidized mixture.

In another embodiment, the sulfur-containing fuel oil is deasphalted prior to contacting the sulfur-containing fuel oil with the water-soluble organic acid. Deasphalting of the sulfur-containing fuel oil may be carried out by methods known to one skilled in the art. Typically, deasphalting is carried out by contacting the sulfur-containing fuel oil with a solvent and filtering or centrifuging the resultant mixture to separate the fuel oil from the insoluble asphaltenes to provide a deasphalted fuel oil. In one embodiment, the inert diluent is selected from the group consisting of liquid saturated hydrocarbons, liquid cyclic hydrocarbons, and mixtures of at least two of the foregoing inert diluents. Suitable non-limiting examples of liquid cyclic hydrocarbons include cyclohexane, cycloheptane, and decalin. Suitable non-limiting examples of liquid saturated hydrocarbons include propane, butane, and petroleum ether. In one embodiment, the method for purifying the sulfur-containing fuel oil further comprises a step of recovering the inert diluent. In one embodiment, the inert diluent is recovered from the first oxidized mixture by distillation, using methods known to one skilled in the art.

In another embodiment, the present invention provides a method for purifying a sulfur-containing fuel oil comprising (a) contacting in a first reaction mixture the sulfur-containing fuel oil comprising dibenzothiophene, benzothiophene, alkyl substituted dibenzothiophenes, and alkyl substituted benzothiophenes with acetic acid and oxygen at a temperature in a range of from about 125° C. to about 175° C., and at a pressure in a range of from about 1500 pounds per square inch to about 2200 pounds per square inch to provide a first oxidized mixture comprising sulfoxides and sulfones of dibenzothiophene, benzothiophene, alkyl substituted dibenzothiophenes, and alkyl substituted benzothiophenes, (b) adding water to provide a biphasic mixture comprising a water-rich phase comprising at least 50 percent of the acetic acid and a fuel oil-rich phase, and (c) separating the water-rich phase from the fuel oil-rich phase to provide a purified fuel oil.

In yet another embodiment, the present invention provides a method for purifying a sulfur-containing fuel oil comprising (a) adding a diluent to the sulfur-containing fuel oil to provide a heterogeneous mixture comprising an asphaltene-rich phase and a first fuel-oil rich phase, (b) separating the asphaltene-rich phase from the first fuel-oil rich phase, (c) contacting the first fuel-oil rich phase with a water-soluble organic acid and oxygen at a temperature in a range of from about 100° C. to about 200° C., and at a pressure in a range of from about 500 pounds per square inch to about 2500 pounds per square inch to provide a first oxidized mixture, (d) adding water to provide a biphasic mixture comprising a water-rich phase and a second fuel oil-rich phase, and (e) separating the water-rich phase from the second fuel oil-rich phase to provide a purified fuel oil.

The following examples are intended only to illustrate methods and embodiments in accordance with the invention, and as such should not be construed as imposing limitations upon the claims.

EXAMPLES

Reagents and catalysts employed herein were obtained from Aldrich Chemical Company and the American Norit Company.

Example 1 to 5 Effect of Oxidative Desulfurization on a Model Mixture Comprising Sulfur Containing Compounds

A model mixture was prepared from tetralin and dioctylsulfide, benzothiophene, and dibenzothiophene (obtained from Aldrich, US) wherein the sulfur-containing compounds were present in a 2:2:3 weight ratio. The model mixture was shown to comprise about 3 weight percent sulfur, when tested using a Varian Saturn 2000 GCMS. 5 milliliters (ml) of the model mixture and acetic acid, or a combination of 5 milliliters (ml) of the model mixture, acetic acid, and Norit activated carbon PAC-20B were placed in each of 6 four-dram vials equipped with magnetic cross-like stirbars and slit TEFLON diaphragm allowing gas access to the vial. The vials were placed in an aluminum heating block. The block with the vials was placed in a one-gallon autoclave equipped with a magnetic stirrer. The autoclave was maintained under an air pressure of 2000 pounds per square inch at a temperature of about 150° C. for a period of about 6 hours. The autoclave was then depressurized and the oxidized samples analyzed using Varian Saturn 2000 GCMS. The results are presented in Table 1. The values in Table 1 are an average of two duplicate runs.

TABLE 1 Oxidation of model mixture having sulfur containing compounds with air in the presence of acetic acid (5 ml. model mixture, 2000 psi air, 150° C., 6 hours). Examples 2 5 Percentage 1 With acetic acid 3 4 With acetic acid converison on With acetic (1 ml) + 50 mg With acetic With acetic (3 ml) + 15 mg oxidation acid (1 ml) Norit carbon acid (2 ml) acid (3 ml) Cu(acac)₂ Dioctylsulfide 96.0 97.2 93.7 98.5 98.0 Benzothiophene 9.4 35.5 42.3 43.8 77.5 Dibenzothiophene 5.6 34.3 33.6 46.8 74.0

Examples 6 to 10 Oxidative Desulfurization of Saudi Crude

Saudi Crude was first subjected to a series of steps described below to obtain oil fractions #1, #2 and #3 containing about 1, 2 and 3 weight percent sulfur respectively. Oil Fraction #3 was obtained as follows. 100 ml of the crude oil was first mixed with petroleum ether (PE) in a volume ratio of PE:Oil equal to 2:1. The mixture was centrifuged at 2100 rpm for 10 min and then decanted to separate the insoluble asphaltenes, to provide about 285 ml of Oil fraction #3 having a sulfur content of about 3 weight percent. Oil fraction #1 and Oil fraction #2 were obtained as follows. 265 ml of Oil fraction #3 obtained above was passed though two sequential columns (0.5 inch diameter), each packed with 4 g adsorbent, Britesorb D350 obtained from PQ Corporation, at a temperature of about 25° C., and at a flow rate of about 1 cubic centimeter/minute, to obtain 110 ml of a first yellow colored fraction containing about 1 weight percent sulfur i.e., Oil fraction #1 and 115 ml of a second orange colored fraction containing about 2 weight percent sulfur i.e., Oil fraction #2.

The three oil fractions so obtained were individually oxidized as in Examples 1 to 5 using a six-pack testing unit. The amounts of oil, acetic acid, activated carbon PAC 20B, and cobalt-manganese oxide on alumina used in the in one or more of Examples 6-10 are included in Table 2 below. Following oxidation, the resulting oxidized mixture was filtered, and the filtrate diluted with water (2 ml). The organic phase was separated, washed with water (2×2 ml) and analyzed on Spectro Phoenix II XRF analyzer to estimate the amount of sulfur in the purified oil. Values for amount of sulfur remaining in the oil after oxidation and yield of oil after purification are provided in Table 2. The values in Table 2 are an average of two runs.

TABLE 2 Oxidative Desulfurization of Crude Oil with Air in the Presence of Acetic Acid, 2000 psi air, 150° C., 6 hours). Initial Final sulfur, sulfur Sulfur Quantity weight weight removed, Oil yield Example Oil of Oil, ml. percent percent percent percent 6 With 50 mg Norit carbon Oil 1 6.8 1.11 1.04 7.0 96.0 Oil 2 6.8 2.07 1.99 4.2 96.1 Oil 3 6.9 2.85 1.70 41.0 87.3 7 With acetic acid (1 ml) + Norit carbon (50 mg) Oil 1 6.8 1.11 0.69 37.8 92.5 Oil 2 6.8 2.07 1.56 24.6 90.1 Oil 3 6.9 2.85 1.31 54.0 82.5 8 With acetic acid (2 ml) + Norit carbon (50 mg) Oil 1 5.4 1.11 0.14 87.6 90.6 Oil 2 5.4 2.07 1.00 51.6 87.7 Oil 3 5.6 2.85 0.87 69.5 79.1 9 With acetic acid (2 ml) + Cobalt oxide/ Manganese oxide/alumina (50 mg) Oil 1 5.4 1.11 0.76 31.9 91.0 Oil 2 5.5 2.07 1.59 25.7 89.5 Oil 3 5.6 2.85 1.19 58.2 80.0 10 With acetic acid (3 ml) Oil 1 4.7 1.08 0.41 61.8 83.8 Oil 2 4.8 1.91 1.08 56.5 86.4 Oil 3 5.0 2.90 0.59 79.8 70.9

Examples 6 to 10 demonstrate that the process of the present invention, generally affords satisfactory sulfur removal and yield of purified crude oil.

Examples 11 and 12 Oxidative Desulfurization of Heavy Fuel Oil

Heavy fuel oil containing 3.465 weight percent sulfur as determined using the Spectro Phoenix II XRF analyzer was diluted with petroleum ether (in a 1:2 volume ratio). A combination of about 10 ml of the diluted oil and acetic acid (4:1 volume ratio) or a combination of about 10 ml of the diluted oil, acetic acid (4:1 volume ratio) and 50 mg catalyst were placed in four-dram vials, and samples were individually oxidized in a similar manner as discussed above in Examples 1 to 5 except that the reaction time was 2 hours. The amounts of oil, acetic acid, and copper acetylacetonate used in the Examples 11 and 12 are included in Table 3 below. Following oxidation, the resulting oxidized mixture was worked up and analyzed using the Spectro Phoenix II XRF analyzer as discussed above in Examples 6 to 10. Values for amount of sulfur remaining in the oil after oxidation and yield of oil after purification are provided in Table 3. The values provided in Table 3 are an average of two runs.

TABLE 3 Oxidative Desulfurization of Crude Oil with Air in the Presence of Acetic Acid, 2000 pounds per square inch air, 150° C., 2 hours. Initial Final sulfur, sulfur Sulfur Quantity weight weight removed, Oil yield Example Oil of Oil, g. percent percent percent percent 11 With acetic acid (2 ml) HFO 5.52 3.465 1.91 44.8 86.1 12 With acetic acid (2 ml) + Cu(acac)₂ (50 mg) HFO 5.51 3.465 1.39 59.9 77.0

Examples 11 and 12 demonstrate the applicability of the process of the present invention to different types of fuel oil and the beneficial effect of copper catalyst in the oxidation process. It should be noted that the experiments conducted as part of this study were not optimized in all cases. Thus it is believed that much higher yields of oil with lower sulfur content than those shown in Table 2 and Table 3 are achievable for heavy fuel oils, by adjusting various reaction parameters which are known to those skilled in the art. Such optimization falls within the scope of the instant invention.

In each of Examples 1 to 12 the oxidized sulfur compounds may be separated from the reaction mixture (first oxidized mixture) using any of the techniques disclosed herein as being effective for that purpose. In one embodiment, the reaction mixture of Example 2 is filtered through a pad of silica gel to remove both the oxidized sulfur compounds and the Norit carbon which may be recovered therefrom.

The foregoing examples are merely illustrative, serving to illustrate only some of the features of the invention. The appended claims are intended to claim the invention as broadly as it has been conceived and the examples herein presented are illustrative of selected embodiments from a manifold of all possible embodiments. Accordingly, it is Applicants' intention that the appended claims are not to be limited by the choice of examples utilized to illustrate features of the present invention. As used in the claims, the word “comprises” and its grammatical variants logically also subtend and include phrases of varying and differing extent such as for example, but not limited thereto, “consisting essentially of” and “consisting of.” Where necessary, ranges have been supplied, those ranges are inclusive of all sub-ranges there between. It is to be expected that variations in these ranges will suggest themselves to a practitioner having ordinary skill in the art and where not already dedicated to the public, those variations should where possible be construed to be covered by the appended claims. It is also anticipated that advances in science and technology will make equivalents and substitutions possible that are not now contemplated by reason of the imprecision of language and these variations should also be construed where possible to be covered by the appended claims. 

1. A method for purifying a sulfur-containing fuel oil, said method comprising: (a) contacting in a first reaction mixture the sulfur-containing fuel oil with a water-soluble organic acid and oxygen at a temperature in a range of from about 100° C. to about 250° C., and at a pressure in a range of from about 15 pounds per square inch to about 2500 pounds per square inch to provide a first oxidized mixture; (b) adding water to provide a biphasic mixture comprising a water-rich phase and a fuel oil-rich phase; and (c) separating the water-rich phase from the fuel oil-rich phase to provide a purified fuel oil.
 2. The method of claim 1, wherein the water-soluble organic acid is selected from the group consisting of acetic acid, formic acid, propionic acid, butyric acid, and mixtures of two or more of the foregoing acids.
 3. The method of claim 1, wherein the water-soluble organic acid is acetic acid.
 4. The method of claim 1, wherein the first reaction mixture further comprises a transition metal oxidation catalyst.
 5. The method of claim 4, wherein the transition metal oxidation catalyst comprises oxides or salts of metals selected from the group consisting of vanadium, manganese, molybdenum, tungsten, cobalt, nickel, copper, and a combination of at least two of the foregoing metals.
 6. The method of claim 5, wherein the transition metal oxidation catalyst comprises an oxide or salt of copper.
 7. The method of claim 4, wherein the transition metal oxidation catalyst is supported on a metal oxide.
 8. The method of claim 7, wherein the metal oxide support is selected from the group consisting of silica, alumina, titania, ceria and a combination of at least two of the foregoing metal oxides.
 9. The method of claim 1, wherein the first reaction mixture further comprises a carbonaceous promoter.
 10. The method of claim 9, wherein the carbonaceous promoter comprises an activated carbon with high surface area.
 11. The method of claim 1, wherein the sulfur-containing fuel oil comprises less than 5 weight percent sulfur.
 12. The method of claim 1, wherein the sulfur-containing fuel oil comprises less than 3 weight percent sulfur.
 13. The method of claim 1, wherein the pressure is in a range of from about 1000 pounds per square inch to about 2250 pounds per square inch
 14. The method of claim 1, wherein the oxygen is provided as a mixture with an inert gas.
 15. The method of claim 14, wherein the oxygen is provided as air.
 16. The method of claim 1, wherein the water-rich phase comprises at least 50 percent of the water-soluble organic acid.
 17. The method of claim 1, further comprising a step of recovering the water-soluble organic acid from the water-rich phase.
 18. The method of claim 17, wherein the water-soluble organic acid is recovered from the water-rich phase by distillation.
 19. The method of claim 1, wherein the sulfur-containing fuel oil comprises dibenzothiophene, benzothiophene, alkyl substituted dibenzothiophenes, and alkyl substituted benzothiophenes.
 20. The method of claim 1, wherein the sulfur-containing fuel oil is deasphalted prior to contacting the sulfur-containing fuel oil with the water-soluble organic acid.
 21. A method for purifying a sulfur-containing fuel oil, said method comprising: (a) contacting in a first reaction mixture a sulfur-containing fuel oil comprising dibenzothiophene, benzothiophene, alkyl substituted dibenzothiophenes, and alkyl substituted benzothiophenes with acetic acid and oxygen at a temperature in a range of from about 130° C. to about 200° C., and at a pressure in a range of from about 1800 pounds per square inch to about 2200 pounds per square inch to provide a first oxidized mixture comprising sulfoxides and sulfones of dibenzothiophene, benzothiophene, alkyl substituted dibenzothiophenes, and alkyl substituted benzothiophenes; (b) adding water to provide a biphasic mixture comprising a water-rich phase comprising at least 50 percent of the acetic acid and a fuel oil-rich phase; and (c) separating the water-rich phase from the fuel oil-rich phase to provide a purified fuel oil.
 22. The method of claim 21, wherein the sulfur-containing fuel oil comprises less than 5 weight percent sulfur.
 23. The method of claim 21, further comprising a step of recovering the water-soluble organic acid from the water-rich phase.
 24. The method of claim 21, wherein the sulfur-containing fuel oil is deasphalted prior to contacting the sulfur-containing fuel oil with the water-soluble organic acid.
 25. A method for purifying a sulfur-containing fuel oil, said method comprising: (a) adding a diluent to the sulfur-containing fuel oil to provide a heterogeneous mixture comprising an asphaltene-rich phase and a first fuel-oil rich phase; (b) separating the asphaltene-rich phase from the first fuel-oil rich phase; (c) contacting the first fuel-oil rich phase with a water-soluble organic acid and oxygen at a temperature in a range of from about 100° C. to about 250° C., and at a pressure in a range of from about 15 pounds per square inch to about 2500 pounds per square inch to provide a first oxidized mixture; (d) adding water to provide a biphasic mixture comprising a water-rich phase and a second fuel oil-rich phase; and (e) separating the water-rich phase from the second fuel oil-rich phase to provide a purified fuel oil. 